Perform epidural injections in heavily sedated or anesthetized animals. The injection site is usually at the lumbosacral space
in dogs and cats and can be performed with a patient in either sternal or lateral recumbency.
Position the patient
Epidural injection is easier to achieve with the patient in sternal recumbency, with the hindlimbs flexed at the hips and
stifles and hocks extended so the legs are positioned alongside the body (Figure 1). This position makes the lumbosacral space easier to identify.
Figure 1. The lumbosacral space is easier to identify if you place the patient in sternal recumbency with the hindlimbs flexed
at the hips, the stifles and hocks extended, and the legs alongside the body.
Palpate the space
Locate the lumbosacral space by palpating the most anterior aspect of both iliac crests with your thumb and middle finger;
the imaginary line connecting them passes through the lumbosacral intervertebral space. With your index finger, palpate the
space as a depression immediately caudal to the dorsal spinous process of L7 and immediately cranial to the fused dorsal spinous
processes of the sacrum (Figure 2).
Figure 2. To identify the lumbosacral space, palpate the iliac crests, dorsal spinous process of L7, and the lumbosacral space
immediately caudal to L7 and cranial to the sacrum.
Prepare the site
Once you have identified the lumbosacral space, clip the hair, and surgically prepare the area. Place a sterile transparent
drape over the area, tear a small opening in the drape at the injection site, and use a sterile disposable 2.5- to 7.5-cm,
20- to 22-ga spinal needle and sterile gloves. If the procedure is being performed in an awake but sedated patient, inject
0.5 to 1 ml 2% lidocaine (with sodium bicarbonate solution added to the local anesthetic in a 1:9 ratio of bicarbonate to
lidocaine to reduce the pain of injection) subcutaneously at the site of the spinal needle insertion and wait five to 10 minutes
before inserting the spinal needle at this site.
Insert the needle
Using your nondominant hand to confirm the landmarks and the lumbosacral space, position the spinal needle over the midline
with your dominant hand (Figure 3). Midline positioning is critical to avoid contact with the transverse processes of the L7 vertebra. Direct the needle bevel
cranially, and advance the needle, with stylet in place, perpendicular to the skin. Position your dominant hand so that it
is in contact with the animal when penetrating the skin to provide counterpressure and to avoid pushing the needle in too
far. It is often helpful to hold the stylet with the index finger of your dominant hand to keep it from being pushed out of
the spinal needle by the subcutaneous tissues. If the needle encounters bone, withdraw it slightly, redirect it caudally or
cranially, and advance it again. You may need to adjust the needle angle to facilitate correct placement in the epidural space.
Figure 3. Once the injection site area is prepared and draped, palpate the lumbosacral space, tear a small opening in the
drape at the injection site, and insert the needle until you penetrate the ligamentum flavum.
The diameter of the lumbosacral epidural space is 2 to 4 mm in medium-sized dogs and < 3 mm in cats.4 As the needle is advanced, you usually feel a popping sensation as the skin is penetrated and then a second pop as the needle
penetrates the ligamentum flavum and enters the epidural space. Advance the needle no farther since most of the blood vessels
lie in the ventral part of the spinal canal and it is more likely that a vessel will be penetrated if advanced too far. In
cats, the spinal dura mater frequently extends to S1-S2, so it is more likely that the dura and arachnoid will be punctured
if the needle is advanced too deeply, entering the subarachnoid space. Occasionally, you will see the tail twitch or hindlimb
movement as the epidural space is entered, indicating the needle has contacted the cauda equina. In this case, the drug may
be injected without redirecting the needle.